Miniature sensors such as gyroscopes useful for measuring or detecting movement or acceleration in particular have been fabricated by micromachining motion sensitive elements in integrated circuit chips. Such devices, based on vibrating mechanical elements which sense rotation, can be produced inexpensively by batch processing and yet yield performance suitable for many applications which require a low cost. One such application, for example, is the detection of yaw for sophisticated controls in automotive vehicles.
One sensor of this type incorporates a micromachined ring which is excited into vibration at its resonant frequency. The direction or orientation of vibration is somewhat dependent on rotation of the sensor so that the vibration can be analyzed to sense directional changes. An array of electrodes capacitively coupled to the ring are used to apply excitation energy and to sense the resulting vibration. Due to slight inaccuracies of fabrication, such rings tend to have two natural resonant frequencies which are close together and which would degrade the Q of the system. Compensation for the ring inaccuracy can be made by applying suitable electrostatic force to the ring, thereby resolving the two resonant frequencies into one and improving the performance of the device.
The application of such electrostatic force involves determining the necessary correction from the sensed vibration and then applying a dc voltage to one, or probably several of the electrodes. To obtain sufficient compensation forces, the device can require either high dc voltages or a large extent of electrode area. These requirements lead to high expense or use of valuable resources; i.e., provision for high voltages increases the cost of the device and the area available for electrodes is limited. The need to use electrodes for other purposes militates against the dedication of sufficient electrode space for compensation by low voltages.